拦截XMLHttpRequest并修改responseText

//// firefox, ie8+//var accessor = Object.getOwnPropertyDescriptor(XMLHttpRequest.prototype, 'responseText');Object.defineProperty(XMLHttpRequest.prototype, 'responseText', {    get: function() {        console.log('get responseText');        return accessor.get.call(this);    },    set: function(str) {        console.log('set responseText: %s', str);        //return accessor.set.call(this, str);    },    configurable: true});//// chrome, safari (accessor == null)//var rawOpen = XMLHttpRequest.prototype.open;XMLHttpRequest.prototype.open = function() {    if (!this._hooked) {        this._hooked = true;        setupHook(this);    }    rawOpen.apply(this, arguments);}function setupHook(xhr) {    function getter() {        console.log('get responseText');        delete xhr.responseText;        var ret = xhr.responseText;        setup();        return ret;    }    function setter(str) {        console.log('set responseText: %s', str);    }    function setup() {        Object.defineProperty(xhr, 'responseText', { get: getter, set: setter, configurable: true        });    }    setup();}